1. Field of the Invention
The present invention relates generally to oscillators and, more particularly, to digitally-controlled reference oscillators.
2. Description of the Related Art
Modern wireless communication systems are used throughout the world and operate over a variety of frequency bands. For example, the global system for mobiles (GSM) has now been accepted in over 140 countries. This system includes the E-GSM 880–915 and 925–960 MHz transmitting and receiving bands for mobiles, 1710–1785 and 1805–1880 MHz transmitting and receiving bands for digital communications services (DCS), and 1850–1910 and 1930–1990 MHz transmitting and receiving bands for United States Personal Communications Services (PCS).
Components of these wireless systems (e.g., cellular telephones) require reference oscillators that can provide demanding technical performance (e.g., high stability, low phase noise and linear response to a tuning potential) while being restricted to occupy a small portion of a communication integrated circuit and being available for extremely low cost (e.g., less than one dollar). Although conventional reference oscillators have met the needs of previous wireless systems, they have generally failed to meet these more demanding requirements.